In recent years, the greenhouse effect due to CO2 is pointed out as a factor of global warming, and thus the measure to cope with this has become an international urgent task in order to protect the global environment. The CO2 generation sources include a various fields of human activities that burn fossil fuels, and a demand for emission limitation of CO2 tends to be even stronger. In association with this, a method to remove and recover CO2 in the flue gas by bringing the flue gas from a boiler into contact with an amine-based CO2 absorbent for example and a method to store the recovered CO2 without releasing it to the atmosphere has been extensively investigated by taking the power generation facilities such as thermal power plants that use great amounts of fossil fuels as the target.
As the method of removing and recovering CO2 from a flue gas using a CO2 absorbent, the following method has been employed. That is, a flue gas is brought into contact with a CO2 absorbent in an absorber, the absorbent which has absorbed CO2 is heated in a regenerator to release CO2 and regenerate the absorbent, and the regenerated absorbent is circulated again in the absorber to be reused (Patent Literature 1: Japanese Patent Application Laid-open No. 2003-225537).
In a method of absorbing, removing, and recovering CO2 from a CO2-containing gas such as a flue gas, it is necessary to add an absorber and a regenerator to a fuel facility for installation. Therefore, cost other than installation cost, for example, operation cost has to be reduced as much as possible. Particularly, when an absorbent is regenerated, a large amount of heat energy (water vapor) is consumed in order to release CO2 from a CO2 absorbent, and therefore a regeneration process needs to be an energy-saving process if possible.
Therefore, the following carbon dioxide recovery system has been conventionally proposed (Patent Literature 2: Japanese Patent Application Laid-open No. 2009-214089). That is, the carbon dioxide recovery system includes a dividing device for dividing a rich solution discharged from an absorber into a first heat exchanger for cooling a lean solution and a second heat exchanger for cooling carbon dioxide-containing vapor. The rich solutions introduced into the first heat exchanger and the second heat exchanger exchange heat with the lean solution and the carbon dioxide-containing vapor, respectively, and then are supplied to a regenerator for releasing CO2.
However, the proposal in Patent Literature 2 has the following problem. That is, the rich solution which has absorbed CO2 is divided on a former stage side of the lean/rich solution heat exchanger as the first heat exchanger, the divided rich solution is supplied to the regenerator while being heated by heat exchange with carbon dioxide-containing vapor discharged from a top of the regenerator, but the divided rich solution is supplied to an upper portion than the rich solution, therefore satisfactory regeneration cannot be performed when the divided rich solution is heated insufficiently, and stable energy-saving cannot be performed. In addition, the absorbent is circulated again, and therefore a cooling efficiency of the lean solution by the rich solution in the lean/rich solution heat exchanger is reduced disadvantageously when a part of the rich solution is divided and extracted on a former stage side of the lean/rich solution heat exchanger. As a result, it is necessary disadvantageously to increase cooling ability to cool the lean solution in a cooler provided before introduction to the absorber.